Extractive distillation of lubricating oil stock



BYIJ. @an Zwemw THEIR ATTORNEY United States Patent O 3,085,062 EXTRACTIVE DISTHLLATION F LUBRICATHNG OIL STCK Vladimir Anastasoli, Houston, Tex., assigner to Shell @il Company, a corporation of Delaware Filed Dec. 10, 1959, Ser. No. 858,654 4 Claims. (Cl. 208-313) This invention relates to an improved method for processing a lube crude to produce lube stocks of reduced aromaticity.

Conventionally, the long residues of lube-containing crudes are vacuum distilled to take overhead a gas oil fraction which is generally passed to a catalytic cracking Zone. Side streams are normally vm'thdrawn from the vacuum distillation zone, such as a 100 distillate, a 250 distillate and a heavy distillate. These distillates are lube stocks which with further processing may be manufactured into lubricatng oils of different viscosities. A short residue is removed from the bottom of the vacuum distillation zone. The lube stocks in the subsequent processing are handled, inter alia, to reduce their aromatic contents. Various processes may be resorted to in achieving aromatic removal, for example, propane extration, phenol extraction, sulfuric acid treatment, duosol extraction and clay treatment. Oftentimes two or more of the foregoing treatments will 'be employed. Phenol extraction (or other polar solvent extraction) is nearly always used in the subsequent processing of lube stock, whatever the combination of steps that may be employed or the sequence resorted to.

lt isan object of this invention to provide an improved process facilitating the removal of armoatics from a lubecontaining stream. This and other objects will become more apparent with the reading of the following description of the process of the invention, taken in conjunction with the drawing containing a single FIGURE which is a process flow diagram of a preferred embodiment of the process.

lt has now been discovered that asphaltic materials such as residual stocks may be advantageously employed as an extractive ydistillation solvent in the vacuum distillation of a long residue of a lube-containing crude. The preparation of the lube stock in this manner for its subsequent liquid-liquid extraction with a polar aromatic selective solvent to remove aromatics remarkably facilitates the latter extraction operation. The asphalt solvent, by lowering the vapor pressure of the aromatics more than that of the normally similarly boiling saturates in the vacuum distillation zone, causes a shift of the aromatics to a lower molecular weight range in each of the distillate cuts as compared to the saturates. This change in distribution is particularly advantageous in the case of the simultaneous production of a plurality of relatively narrow boling range lube distillate fractions. Subsequent extraction of the individual distillates is therefore easier because a polar aromatic selective solvent, such as phenol or furfural, preferentially dissolves lower molecular weight materials as well as aromatics. That is to say, the appearance of the aromatic hydrocarbons in the lube distillates as lower molecular weight materials permit their more ready separation from the lube distillate undergoing liquid-liquid extraction. In addition to this subsequent processing advantage, the quality of the oil product is believed to be improved since it is possible i `v`to remove undesirable high molecular weight polyaromatics which with conventional processing cannot be removed completely by extraction Without also removing desirable lube components. This increased ease in the subsequent polar solvent extraction permits there a reducice tion in solvent to feed ratio and also results in less loss of lube materials to the aromatic extract phase.

The asphaltic solvent is supplied to the vacuum distillation zone in a solvent to feed ratio (weight basis) in excess of 0.75. Lesser solvent to feed ratios are substantially ineffective and are of no commercial value. Preferably the solvent is employed in 1.0 to 3 times the weight of feed. The solvent is preferably introduced to an upper level of the vacuum distillation zone and at a point above the highest lube stock take-off. The lube stock side streams are removed preferably as vapor, thus avoiding asphalt contamination which could occur if liquid take-oifs were used. However, liquid side stream draw-o1s may be used followed by separate distillation to separate the lube stock components from the asphalt agent. This is more readily done for the lighter or lower boiling cuts than the highest boiling cut. Following separate distillation of a given side stream, the separated asphalt agent is suitably returned to the next lower point (e.g. tray) in the primary extractive distillation zone.

The highly asphaltic extractive distillation solvent used in the process may be obtained from several sources. For example, either reduced virgin stock or materials prepared from catalytically cracked or thermally cracked heavy ends. Suitablematerials are characterized by high molecular weights of greater than 750, an API gravity of less than 15, and are made up to a large part of condensed aromatic compounds. Among the preferred asphaltic materials are the virgin residual stocks obtainable from a reduced crude flashing unit. Secondary flasher pitches are especially suitable. The asphaltic solvents useful in the process are composed at least to the extent of of their total weights of materials having an atmospheric boiling point in excess of 850 F. The flasher pitches are readly available and will be generally used in preference to the synthetic asphalts prepared from the cracked sources. Asphaltic solvents obtained from the propane deasphalting of lube vacuum residues are preferred even over the iiasher pitches.

The asphaltic solvents may be obtained from a thermally cracked residuum commonly available in refining operations via a vacuum distillation or propane deasphalting to remove the lower boiling components. The asphaltic material can be prepared from a high boiling catalytically cracked source, preferably a clarified oil. As in the instance of the thermally cracked residuum, the clariiied oil may be either propane deasphalted or vacuum distilled to separate the lower boiling components therefrom.

The conditions of the vacuum distillation in the presence of the asphaltic solvent do not differ significantly from those conditions normally employed in the vacuum distillation zone. The distillation zone is preferably maintained at a subatmospheric pressure withn the range of 25 to 760 mm. Hg, preferably less than '100 mm. Hg, and a bottom temperature in the range of 400 F. to 800 F. The top operating temperature is in the range of 300 F. to 750 F., preferably in excess of 400 F. Ihe asphalt is best supplied to the top of the vacuum distillation zone at a temperature within the range of 300 to 800 F. The long residue may be supplied at a temperature in the range of 400 to 800 F.

The incidental equipment including pumps, valves, instrumentation, heat exchangers, reboilers, etc. being conventional are not specifically referred to in the following example nor illustrated in the drawing.

In the iiow diagram of the drawing, a long residue owing in a line l0 is fed to a bottom section of a vacuum distillation column lf2. Asphaltic solvent in a solvent to feed ratio in the preferred range of 1.0 to 3 is supplied via a line j13 to an upper portion of the distillation column above the top takeoff of the lube distillate streams. The particular solvent used is an asphalt derived from the propane deasphalting of a lube vacuum residue. It will be noted that the asphalt line enters at a point some distance below the overhead gas oil removal line. Preferably there is a tray or two separating the asphalt entry line and the gas oil take-oil line to avoid contamination of the gas oil vapors with the asphaltic material.

The highly asphaltic solvent reduces the volalilityY of the monoand poly-aromatics relative to the normal paraftins. This alteration in volatility of the components of the long residue promotes a shift to a lower molecular weight range of aromatics in each of the lube stock streams withdrawn from the vacuum distillation zone. A light distillate, such as a l() distillate fraction, is removed in a vapor take-olf line 115 to a condenser 16 out of which the condensate is collected in an accumulator 17. An intermediate distillate, such as a 2501 distillate fraction, is removed in a side vapor line 18 to a condenser 19 and accumulator 2t). Lubricating oils having viscosities of 100 and 250 Saybolt seconds Universal at 100 are produced respectively from the l0() and 250` distillate fractions. Likewise, a heavy distillate is taken from a lower level of the vacuum distillation zone in a vapor take-olf line 2.2 to a condenser 23. The condensate out of the condenser collects in an accumulator 24. A short residue in mixture with the asphaltic solvent and extracted material is removed from the bottom of the vacuum distillation zone 12 in a line 26. In the process flow diagram of the drawing, for simplicity, only one of the lube stocks, namely, the 100 distillate, is illustrated as being passed to a following liquid-liquid extraction. The 250 distillate and the heavy distillate will normally be handled in the same fashion. The 100 distillate condensate leaves the accumulator 17 in a line 27 and is introduced to a lower section of a conventional liquid-liquid extraction zone 28. Various polar solvents, commonly used for such extractions, may be employed as the extractant. Phenol and furfural are perhaps the solvents most widely used. In this example a lean phenol stream is introduced to an upper portion of the extraction zone via a line 30. The phenol passes in countercurrent ow downwardly through the extraction zone to the 100l distillate, serving to selectively extract the aromatic content of that distillate. A lube stock rainate of reduced aromaticity is removed from the top of the zone in a line 3,1. The extract phase made up of the phenol solvent and extractedl aromatic hydrocarbons leaves the extraction zone in a line 32 and is passed to a lower section of `a solvent stripper 33. The solvent stripper is operated to pass overhead a vapor stream of the stripped solvent. The lean solvent is returned to the extraction zone in the aforementioned line 30. The conditions attending the operation of the liquid-liquid extraction zone and of the CFI i solvent stripper are conventional. The aromatic extract is removed from the stripping zone in a line 34.

The short residue stream of line 26 is passed to a conventional propane deasphalting 36 where a deasphalted oil is separated and removed in a line 37. The asphalt product from the deasphalting zone is recycled in part through line 13 to the extractive distillation zone, with the remainder of the asphalt being withdrawn from the system in a take-oli line 39.

I claim as my invention:

1. In a process for the production of a lube stock of low aromaticity from a long residue of a lube containing crude, wherein the long residue is subjected to a vacuum distillation to produce an aromatic-containing lube stock stream and a short residue, which lube stock stream is passed to further processing to reduce its aromatic content, the improvement comprising (1) carrying on the vacuum distillation under extractive distillation conditions in the presence of an asphaltic solvent in liquid phase, thereby promoting a shift to a lower molecular weight range of aromatics in said lube stock stream compared to that occurring in a vacuum distillation in the absence of said asphaltic solvent, said asphaltic solvent being supplied to the vacuum distillation zone in a solvent to feed ratio in excess of 0.75 (2) passing the lube stock stream from the distillation zone to a liquid-liquid extraction zone; and (3) there subjecting the lube stock to an extraction with a polar aromatic selective solvent to reduce its aromatic content, said extraction being carried on with signicantly more ease due to the shift in the molecular weight range of the aromatic content of the lube stock.

2. A process in accordance with claim l wherein the asphaltic solvent to feed ratio is in the range 0f 1.0 to 3.

3. A process in accordance with claim 1 wherein the asphaltic solvent is composed at least to the extent of of its total weight of materials having an atmospheric boiling point in excess of 850 F.

4. A process in accordance with claim l wherein the asphaltic solvent is an asphalt from the propane deasphalting of a lube vacuum residue.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Asphalts and Allied Substances, Abraham; 5th edition, vol 1; D. Van Nostrand Co. Inc., publishers, 1954; pages 1735-137. 

1. IN A PROCESS FOR THE PRODUCTION OF A LUBE STOCK OF LOW AROMATICITY FROM A LONG RESIDUE OF A LUBE CONTAINING CRUDE, WHEREIN THE LONG RESIDUE IS SUBJECTED TO A VACUUM DISTILLATION TO PRODUCE AN AROMATIC-CONTAINING LUBE STOCK STREAM AND A SHORT RESIDUE, WHICH LUBE STOCK STREAM IS PASSED TO FURTHER PROCESSING TO REDUCE ITS AROMATIC CONTENT, THE IMPROVEMENT COMPRISING (1) CARRYING ON THE VACUUM DISTILLATION UNDER EXTRACTIVE DISTILLATION CONDITIONS IN THE PRESENCE OF AN ASPHALTIC SOLVENT IN LIQUID PHASE, THEREBY PROMOTING A SHIFT TO A LOWER MOLECULAR WEIGHT RANGE OF AROMATICS IN SAID LUBE STOCK STREAM COMPARED TO THAT OCCURRING IN A VACUUM DISTILLATION IN THE ABSENCE OF SAID ASPHALTIC SOLVENT, SAID ASPHALTIC SOLVENT BEING SUPPLIED TO THE VACUUM DISTILLATION ZONE IN A SOLVENT TO FEED RATIO IN EXCESS OF 0.75; (2) PASSING THE LUBE STOCK STREAM FROM THE DISTILLATION ZONE TO A LIQUID-LIQUID EXTRACTION ZONE; AND (3) THERE SUBJECTING THE LUBE STOCK TO AN EXTRACTION WITH A POLAR AROMATIC SELECTIVE SOLVENT TO REDUCE ITS AROMATIC CONTENT, SAID EXTRACTION BEING CARRIED ON WITH SIGNIFICANTLY MORE EASE DUE TO THE SHIFT IN THE MOLECULAR WEIGHT RANGE OF THE AROMATIC CONTENT OF THE LUBE STOCK. 